This invention relates to a device for measuring the flow rate of a gas. For example, this invention relates to a device for measuring the flow rate of intake air in an internal combustion engine.
There has been proposed a device for measuring the flow rate of intake air in an internal combustion engine which device comprises an electric heater disposed in an air intake pipe of an internal combustion engine, and a pair of temperature dependent resistors located upstream and downstream respectively of the electric heater. In the device, the quantity of heat generated from the electric heater is controlled to maintain a constant temperature difference .DELTA.T between the temperatures of the two temperature dependent resistors, so that the flow rate of intake air, which is the gas whose flow rate is to be measured, can be measured on the basis of the quantity of electric power supplied to the electric heater.
In such a prior art device, a voltage comparison circuit and an integrating circuit are employed in its measuring circuit so that the temperature difference .DELTA.T between the temperatures of the temperature dependent resistors can be controlled to be constant. The prior art device having the above construction has however been disadvantageous in that the accuracy of measurement is not so high and the system response is also insufficient due to the presence of a considerable proportion of ripples in the output waveform.